1. Technical Field
The present invention relates to ultrasonic endoscopic probes in medical equipment and the like for acquiring, for observation, ultrasonic waves reflected by a tested specimen irradiated with ultrasonic waves radiated from an ultrasonic transducer rotated by a motor built inside the tip of the probe.
2. Related Art
Diagnostic imaging technology is widely utilized in the fields of analysis, medicine and the like. For example, in the medical or precision device manufacturing field, various diagnostic imaging techniques are being researched and utilized, in addition to the conventional observations using cameras. Examples of such diagnostic imaging technologies include X-ray CT and nuclear magnetic resonance systems that enable tomographic imaging, ultrasonic diagnostic devices that capture ultrasonic reflections, and optical coherence tomography systems utilizing the coherence of light. One of the tomographic imaging systems that have been most extensively utilized in recent years is the ultrasonic diagnostic device characterized by its relatively deep scan depth.
An ultrasonic transducer used in the ultrasonic diagnostic device has an oscillation frequency of the order of 10 to 20 MHz in conventional devices, with the wavelength of several tens of μm. Thus, compared with the optical coherence tomography system in which the light source uses near-infrared light with the wavelength of 1.3 micron, the ultrasonic diagnostic device is disadvantageous in that the spatial resolution required of a diagnostic device is not easily achievable due to the longer wavelength. However, it has become possible in recent years to increase the oscillation frequency of the ultrasonic transducer up to 300 MHz or above, with the wavelength having been improved to the level comparable to that of near-infrared light used in optical coherence tomography. Ultrasonic diagnosis is non-invasive to living bodies and is now capable of identifying objects with the spatial resolution of approximately 10 μm (microns). Thus, there are expectations that, particularly in the medical field, the ultrasonic diagnostic device can be built inside the thin tip portion of an endoscope and utilized for the discovery, diagnosis, or treatment of an affected area in the stomach, the small intestine, the arterial vessels and the like of the human body. Representative structures of the ultrasonic endoscope in which the ultrasonic diagnostic imaging technology is applied are discussed in JP-A-2010-131387 and U.S. Pat. No. 8,211,025 B2, for example.
In the ultrasonic endoscope described in JP-A-2010-131387, as shown in FIG. 2 of the literature, an output drive shaft 51 of a micromotor 41 is provided with a barrier membrane film seal 60 for isolating an acoustic coupling fluid 29, which entirely covers a transducer 53, from the micromotor 41, thus preventing the entry of the acoustic coupling fluid 29 into the micromotor 41. From the transducer, ultrasonic waves are radiated onto the tested specimen, and a reflected ultrasonic waveform is captured by the transducer, enabling the observation of the state of the tested specimen.
However, as the micromotor 41 starts rotation, the internal air expands as the temperature increases, and the air may enter via a gap of the barrier membrane film seal 60 into the acoustic coupling fluid 29, producing air bubbles therein. In the ultrasonic endoscope, the air bubbles in the acoustic coupling fluid 29 would reflect the ultrasonic waves radiated from the transducer, preventing the ultrasonic waves from reaching the tested portion located further ahead and interfering with observation.
In U.S. Pat. No. 8,211,025 B2, as shown in FIG. 3 of the literature, a gear box and a motor 320 are disposed in a fluid-filled portion of a catheter body 360 filled with acoustic coupling fluid. A shaft 340 of the motor 320 causes an ultrasonic transducer 310 to rotate in an oscillatory manner at certain angles. From the transducer 310, ultrasonic waves are radiated toward the tested specimen, and a reflected ultrasonic waveform is captured by the transducer 310 to observe the state of the tested specimen.
In this structure, lubrication oil or grease previously injected into the motor bearings may dissolve into the acoustic coupling fluid, degrading the transmission characteristics of the acoustic coupling fluid. Further, the antifoaming performance of the acoustic coupling fluid may be hampered by chemical reaction, producing air bubbles and interfering with observation of the tested portion. In addition, lubrication of the motor bearings may be adversely affected, causing frictions in the bearings and producing uneven rotation speed or an increase in the amount of oscillation. As a result, the transducer 310 may become unable to sufficiently transmit or receive ultrasonic waves, resulting in deterioration in the observed image or preventing the acquisition of the spatial resolution required by the ultrasonic endoscope.